The present invention relates to a technology for machining an object by generating an electric discharge between the object and an electrode. More particularly, this invention relates to a technology for controlling a jump operation in which distance between the object and the electrode is temporarily increased at each of predetermined times or depending on the machining state.
Conventionally, an electric discharge machining device performs a jump operation. This jump operation is an operation in which distance between the object and the electrode (xe2x80x9cinterelectrode distancexe2x80x9d) is temporarily increased at each of predetermined times or depending on the machining state. Machining waste deposited between the electrode and the object can be removed efficiently because of this jump operation. Moreover, speed or precision of electric discharge machining can be improved.
FIG. 14 is a block diagram showing the configuration of a conventional electric discharge machining device. Moreover, FIGS. 15(a)-15(d) are time charts for explaining a jump operation performed by the conventional electric discharge machining device. FIG. 15(a) is a time chart showing a change in interelectrode distance in the jump operation, FIG. 15(b) is a time chart showing a change in speed in the jump operation, FIG. 15(c) is a time chart showing a change in acceleration in the jump operation, and FIG. 15(d) is a graph showing a result of Fourier transform of the time chart in FIG. 15(a).
Referring to FIG. 14, the interelectrode voltage detection unit 7 detects a voltage between the electrode 11 and the object 12 (xe2x80x9cinterelectrode voltagexe2x80x9d). The interelectrode servo control unit 3 controls the position of the main shaft 13 according to the detected interelectrode voltage. Moreover, the interelectrode servo control unit 3 performs electric discharge machining of the object 12 by using an electric discharge phenomenon. The jump control unit 102 controls temporarily increasing the interelectrode distance at each of predetermined times or depending on the machining state. Whether machining by the interelectrode servo control unit 3 is to be performed or a jump operation by the jump control unit 102 is to be performed can be selected with the switching unit SW10. When the jump control unit 102 performs a jump operation, the jump control unit 102 notifies the interelectrode servo control unit 3 the jump operation is to be performed, and switches the switching unit SW10 from the interelectrode servo control unit 3 to the jump control unit 102.
The jump operation will be described below with reference to FIGS. 15(a)-15(d). The jump control unit 102 starts the jump operation at a point of time at which a predetermined time has elapsed or a point of time t1 at which a predetermined machining state is set. In the jump operation, the electrode 11 is raised at a speed V1 until the interelectrode distance changes from a distance l1 to a distance l2. At a point of time t2 at which the interelectrode distance is distance l2, the electrode 11 is switched from an up state to a down state to move the electrode 11 downward at a speed xe2x88x92V1. At a point of time at which the interelectrode distance is a distance l3, the speed xe2x88x92V1 of the of the electrode 11 is changed into the speed xe2x88x92V2, and the electrode 11 is reduced in speed, and the interelectrode distance returns to the distance l1. At the point of time t3, the speed xe2x88x92V1 is reduced to the speed xe2x88x92V2 because the electrode 11 may collide with the object to be machined 12 by inertia of the electrode 11 when the electrode 11 is moved downward at the speed xe2x88x92V1.
In this conventional electric discharge machining device, since the speed is sharply changed at the points of time t1, t2, and t3, the response of a mechanical control system is delayed, or a target is overshot. In addition, since the locus of the interelectrode distance is a locus containing a high-frequency component, a resonance of the mechanical system is excited, and vibration remains after the jump operation is completed. In this case, since the electric discharge machining is performed by applying a voltage across the electrodes in a state in which the interelectrode distance between the electrode 11 and the object to be machined 12 is kept at several xcexcm to tens of xcexcm, a problem that machining precision or speed is considerably decreased by slight residual vibration is posed.
Moreover, conventionally, a deceleration distance (l3xe2x88x92l1) may be increased to prevent machining precision from being degraded by the influence of residual vibration or the overshooting of the shaft. However, in this case, it takes long time to perform the jump operation, and a problem that the entire machining time is extended is posed.
More specifically, a jump operation performed by the conventional electric discharge machining device has a problem in machining precision or machining speed is considerably decreased depending on a setting of residual vibration or deceleration distance because speed or acceleration is sharply changed.
In fact, with respect to the object 12 to be machined and the electrode 11, an optimum set frequency and the allowable maximum component value of the frequency in the jump operation change, depending on the mass of the electric discharge machining device, a machining condition, aging of the electric discharge machining device, and the like. In this case, when these two elements are adjusted, the machining time is shortened, and the machining precision can be increased. It is hard for an operator of the electric discharge machining device to adjust the set frequency and the allowable maximum component value optimally.
This invention has been made to solve the above problems, and has as its object to obtain an electric discharge machining device and an electric discharge machining method which can shorten machining time and which can improve a machining precision.
In order to solve the this problem, the electric discharge machining device according to this invention comprises an interelectrode servo control unit which controls an interelectrode distance which is a distance between an electrode and an object to be machined while applying a predetermined voltage across the electrode and the object; and a jump control unit which controls a jump operation in which the interelectrode distance is temporarily increased at every predetermined time or depending on a machining state. The jump control unit includes a command locus generation unit which generates a smooth command locus having a frequency component in a predetermined frequency range which is not higher than a predetermined frequency or lower than the predetermined frequency. The jump control unit controls the jump operation by using a smooth command locus generated by the command locus generation unit. For example, since the command locus generation unit is designed to generate a command locus by using a sine wave having a low-frequency component which is lower than a resonance frequency of a mechanical system, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining device according to another invention comprises an interelectrode servo control unit which controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object; and a jump control unit which controls a jump operation in which the interelectrode distance is temporarily increased at every predetermined time or depending on a machining state. The jump control unit includes a command locus generation unit which generates a smooth command locus having a frequency component in a predetermined frequency range except for a frequency range of a first frequency which is lower than a predetermined frequency to a second frequency which is higher than the predetermined frequency. The jump control unit controls the jump operation by using the smooth command locus generated by the command locus generation unit. For example, since the command locus generation unit is designed to generate a command locus by using a sine wave having a frequency component sufficiently different from a resonance frequency of a mechanical system, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining device according to still another invention comprises an interelectrode servo control unit which controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object; and a jump control unit which controls a jump operation in which the interelectrode distance is temporarily increased at every predetermined time or depending on a machining state. The jump control unit includes a command locus generation unit which generates a smooth command locus in which a value of a frequency component in a predetermined frequency range which is not lower than a predetermined frequency or higher than the predetermined frequency is suppressed to a value which is not larger than a predetermined value or smaller than the predetermined value. The jump control unit controls the jump operation by using the smooth command locus generated by the command locus generation unit. For example, since the command locus generation unit is designed to generate a smooth command locus in which a high frequency component which is higher than a resonance frequency of a mechanical system is suppressed to a value which is not larger than a predetermined value, vibration of the mechanical system does not remain upon completion of the jump operation, precise machining can be performed, and a deceleration distance of the electrode can be decreased by decreasing vibration and decreasing an amount of overshooting. As a result, time required for the entire jump operation can be shortened, and machining speed can be increased.
The electric discharge machining device according to still another invention comprises an interelectrode servo control unit which controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object; and a jump control unit which controls a jump operation in which the interelectrode distance is temporarily increased at every predetermined time or depending on a machining state. The jump control unit includes a command locus generation unit which generates a smooth command locus in which a value of a frequency component in a predetermined frequency range of a first frequency which is lower than a predetermined frequency to a second frequency which is higher than the predetermined frequency is suppressed to a value which is not larger than a predetermined value or smaller than the predetermined value. The jump control unit controls the jump operation by using the smooth command locus generated by the command locus generation unit. For example, since the command locus generation unit is designed to generate a smooth command locus in which a value of a frequency component approximate to a resonance frequency of a mechanical system, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
In the electric discharge machining device according to the above invention, the jump control unit further includes a filter, and the filter shapes a locus into a smooth locus in which the value of the frequency component in the predetermined frequency range is suppressed to a value which is not larger than the predetermined value or smaller than the predetermined value. For example, since an analog filter is arranged as the filter to generate a smooth command locus in which a high frequency component which is higher than a resonance frequency of a mechanical system is suppressed to a value which is not larger than a predetermined value, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed. An deceleration distance of the electrode can be shortened by reducing vibration and reducing an amount of overshooting. As a result, time required for the entire jump operation can be shortened, and machining speed can be increased.
In the electric discharge machining device according to the above invention, the command locus generation unit adds a plurality of loci in each of which the value of the frequency component in the predetermined frequency range is suppressed to a value which is not larger than a predetermined value or smaller than the predetermined value to each other to generate the smooth command locus which is suppressed to the value which is not larger than the predetermined value or smaller than the predetermined value. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining device according to the above invention further includes a storage unit which stores condition information of the jump operation including the predetermined frequency range or the predetermined frequency range and the predetermined value, and the command locus generation unit is designed to generate the smooth command locus on the basis of the predetermined frequency range or the predetermined frequency range and the predetermined value, so that the jump operation can be flexibly changed and set.
The electric discharge machining device according to the above invention further includes setting input unit which inputs values of the predetermined frequency range or at least one of the predetermined frequency range and the predetermined value, and the command locus generation unit generates the smooth command locus on the basis of the predetermined frequency range or the predetermined frequency and the predetermined value set by the setting input unit. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, so that precise machining can be easily set.
In the electric discharge machining device according to the above invention, the jump control unit further includes a jump operation evaluation unit which detects a state in the jump operation to evaluate the jump operation, and a setting change unit which changes the set values of the predetermined frequency range, the predetermined value, or the predetermined frequency range and the predetermined value on the basis of an evaluation result obtained by the jump operation evaluation unit. In this manner, the jump operation evaluation unit evaluates an actual motion of the electrode, and the setting change unit automatically change a setting on the basis of the evaluation result to obtain an optimum machining condition such as the predetermined frequency range or the predetermined value. For this reason, machining at a high speed and a high precision can be automatically performed.
In the electric discharge machining device according to the above invention, the command locus generation unit generates a predetermined function which satisfies the predetermined frequency range or the predetermined frequency range and the predetermined value and which corresponds to the jump operation, and performs at least one integrating processor at least one differential process to the predetermined function to generate the command locus or a control command corresponding to the command locus. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, and precise machining can be performed. Moreover, deceleration distance of the electrode can be shortened by reducing vibration and reducing an amount of overshooting. As a result, time required for the entire jump operation can be shortened, and machining speed can be increased.
In the electric discharge machining device according to the above invention, the jump control unit controls the jump operation on the basis of a command speed or a command acceleration corresponding to the smooth command locus. In this manner, flexible electric discharge machining can be performed at a high speed and high precision.
The electric discharge machining method according to still another invention in which an interelectrode servo control unit controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object and a jump control unit controls a jump operation temporarily increases the interelectrode distance every predetermined time or depending on a machining state. The method comprises the command locus generation step of generating a smooth command locus having a frequency component in a predetermined frequency range which is not higher than a predetermined frequency or lower than the predetermined frequency, and the jump operation control step of controlling the jump operation by using a smooth command locus generated by the command locus generation step. For example, since the command locus generation step is designed to generate a command locus by using a sine wave having a low-frequency component which is lower than a resonance frequency of a mechanical system, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining method according to still another invention in which an interelectrode servo control unit controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object and a jump control unit controls a jump operation temporarily increases the interelectrode distance every predetermined time or depending on a machining state. The method comprises the command locus generation step of generating a smooth command locus having a frequency component in a predetermined frequency range except for a frequency range of a first frequency which is lower than a predetermined frequency to a second frequency which is higher than the predetermined frequency, and the jump operation control step of controlling the jump operation by using the smooth command locus generated by the command locus generation step. For example, since the command locus generation step is designed to generate a command locus by using a sine wave having a frequency component sufficiently different from a resonance frequency of a mechanical system, vibration of the mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining method according to still another invention in which an interelectrode servo control unit controls an interelectrode distance which is a distance between an electrode and an object while applying a predetermined voltage across the electrode and the object and a jump control unit controls a jump operation temporarily increases the interelectrode distance every predetermined time or depending on a machining state. The method comprises the command locus generation step of generating a smooth command locus in which a value of a frequency component in a predetermined frequency range which is not lower than a predetermined frequency or higher than the predetermined frequency is suppressed to a value which is not larger than a predetermined value or smaller than the predetermined value, and the jump control step of controlling the jump operation by using the smooth command locus generated by the command locus generation step. For example, since the command locus generation step is designed to generate a smooth command locus in which a value of frequency component approximate to a resonance frequency of a mechanical system is suppressed to a value which is not larger than a predetermined value, vibration of the mechanical system does not remain upon completion of the jump operation, precise machining can be performed.
In the electric discharge machining method according to the above invention, the command locus generation step includes the addition step of adding a plurality of loci in each of which the value of the frequency component in the predetermined frequency range is suppressed to a value which is not larger than a predetermined value or smaller than the predetermined value to each other, and the generation step of generating the smooth command locus which is suppressed to the value which is not larger than the predetermined value or smaller than the predetermined value on the basis of the loci added by the addition step. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, and precise machining can be performed.
The electric discharge machining method according to the above invention further includes the setting input step of inputting a setting of the predetermined frequency range or at least one of the predetermined frequency range and the predetermined value, and the command locus generation step generates the smooth command locus on the basis of the predetermined frequency range or the predetermined frequency and the predetermined value set by the setting input step. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, so that precise machining can be easily set.
The electric discharge machining method according to the above invention further includes the jump operation evaluation step of detecting a state in the jump operation to evaluate the jump operation, and the setting change step of changing a setting of the predetermined frequency range, the predetermined value, or the predetermined frequency range and the predetermined value on the basis of an evaluation result obtained by the jump operation evaluation step. In this manner, the jump operation evaluation step evaluates an actual motion of the electrode, and the setting change step automatically change a setting on the basis of the evaluation result to obtain an optimum machining condition such as the predetermined frequency range or the predetermined value. For this reason, machining at a high speed and a high precision can be automatically performed.
In the electric discharge machining method according to the above invention, the command locus generation step generates a predetermined function which satisfies the predetermined frequency range or the predetermined frequency range and the predetermined value and which corresponds to the jump operation, and performs at least one integrating processor at least one differential process to the predetermined function to generate the command locus or a control command corresponding to the command locus. In this manner, vibration of a mechanical system does not remain upon completion of the jump operation, and precise machining can be performed. Moreover, deceleration distance of the electrode can be shortened by reducing vibration and reducing an amount of overshooting. As a result, time required for the entire jump operation can be shortened, and machining speed can be increased.
In the electric discharge machining device according to the above invention, the jump operation control step controls the jump operation on the basis of a command speed or a command acceleration corresponding to the smooth command locus. In this manner, flexible electric discharge machining can be performed at a high speed and a high precision.